There is a rating between 0-255 I believe, or 0-128 and players between 0-30 would be very defensive, between 30-60 defensive or something similar to that. It definitely varies and is just converted into text, however the rating is only a preference and does not portray how good a batsman may be at being very aggressive. You may have a quality slogger like Albie Morkel or a terrible slogger like Shahid Afridi but they will both be portrayed as very aggressive, it is only their batting rating that decides it.
Another issue that was teasing me from ICC09 has recently come to my attention again. I don't believe we have found everything that is possible to be edited. When you are choosing bowling technique training you have the option to choose accuracy, defensive bowling and aggressive bowling. This means there must also be levels for these as well, instead of just the single bowling rating that we have found.
Looks like we might need to keep searching!